<template>
    <ul class="list">
        <li class="item" 
        v-for="item of letters" 
        :key="item" @click="handleLetterClick" @touchstart="handleTouchStart" @touchmove="handleTouchMove" @touchend="handleTouchEnd" :ref="item">
        {{item}}
        </li>
    </ul>
</template>

<script>
export default {
    name:'CityAlphabet',
    props:{
        cities: Object
    },
    computed:{
        letters(){
            const letters = []
            for(let i in this.cities){
                letters.push(i)
            }
            return letters
        }
    },
    data() {
        return {
            touchStatus:false,
            startY:0,
            timer:null
        }
    },
    updated() {
        this.startY = this.$refs['A'][0].offsetTop
    },
    methods:{
        handleLetterClick(e){
            this.$emit('change',e.target.innerText)
        },
        handleTouchStart(){
            this.touchStatus = true
        },
        handleTouchMove(e){
            if(this.touchStatus){
                if(this.timer){
                    clearTimeout(this.timer)
                }
                this.timer = setTimeout(()=>{
                    const startY = this.$refs['A'][0].offsetTop
                    const touchY = e.touches[0].clientY - 79
                    const index = Math.floor((touchY - this.startY) / 20)
                    if(index>=0 && index<this.letters.length){
                        this.$emit('change',this.letters[index])
                    }
                },16)
            }
        },
        handleTouchEnd(){
            this.touchStatus = false
        }
    }
}
</script>

<style lang="stylus" scoped>
  @import '~styles/varibles.styl';
  .list
    display flex
    flex-direction column
    justify-content center
    position absolute
    top 1.5rem
    right 0
    bottom 0
    width .4rem
    .item
      line-height .4rem
      text-align center
      color $bgColor
</style>